CN-122026725-A - Power conversion circuit and control method thereof

Abstract

The invention provides a power conversion circuit and a control method thereof, the resonant power conversion circuit for converting an input voltage to an output voltage comprises a resonant capacitor, a transformer, an upper bridge transistor, a lower bridge transistor and a control circuit. The resonance capacitor is coupled between the resonance node and the ground terminal, and the resonance node generates resonance voltage. The transformer includes a primary coil and a secondary coil coupled between the switching node and the resonant node. The upper bridge transistor provides an input voltage to the switching node. The lower bridge transistor couples the switching node to ground. When the upper bridge transistor and the lower bridge transistor are turned off, the control circuit judges that the resonance voltage is smaller than a preset threshold value, and then drives the upper bridge transistor and the lower bridge transistor.

Inventors

• YANG DAYONG
• LIN ZICHENG
• LIU GUOJI
• Lin Kunye

Assignees

• 立锜科技股份有限公司

Dates

Publication Date

20260512

Application Date

20250916

Priority Date

20250721

Claims (20)

1. 1. A power conversion circuit for converting an input voltage to an output voltage, comprising: The resonance capacitor is coupled between a resonance node and a grounding end, wherein the resonance node generates resonance voltage; A transformer including a primary coil and a secondary coil, wherein the primary coil is coupled between a switching node and the resonant node; an upper bridge transistor for providing the input voltage to the switching node based on an upper bridge driving signal; a lower bridge transistor for coupling the switching node to the ground terminal based on a lower bridge driving signal, and The control circuit generates the upper bridge driving signal and the lower bridge driving signal based on the output voltage and the resonance voltage; when the upper bridge transistor and the lower bridge transistor are turned off, the control circuit judges that the resonance voltage is smaller than a preset threshold value, and then drives the upper bridge transistor and the lower bridge transistor.
2. 2. The power conversion circuit according to claim 1, wherein a discharge rate of the output voltage is faster than a discharge rate of the resonance capacitor.
3. 3. The power conversion circuit of claim 1, further comprising: a first discharge circuit for discharging the resonant capacitor, and And the second discharging circuit discharges the output voltage.
4. 4. The power conversion circuit of claim 3, wherein the first discharge circuit further comprises: a detection resistor coupled to the resonance node, and The discharging resistor is coupled between the detecting resistor and the grounding end; the control circuit adjusts the resistance value of the discharge resistor to adjust a discharge current for discharging the resonance capacitor.
5. 5. The power conversion circuit according to claim 4, wherein the resonance voltage is divided by the detection resistor and the discharge resistor to generate a control voltage; Wherein the control circuit further comprises: an analog-to-digital converter for converting the control voltage to a digital code; wherein the control circuit determines whether the resonance voltage is less than the predetermined threshold value based on the digital code; When the control circuit judges that the resonance voltage is smaller than the preset threshold value, the control circuit generates the upper bridge driving signal and the lower bridge driving signal.
6. 6. The power conversion circuit of claim 3, further comprising: a rectifying circuit for converting the energy of the secondary coil into the output voltage based on a gate signal, and A secondary control circuit for generating the gate signal; Wherein the secondary control circuit enables a discharge signal when the output voltage exceeds a first voltage threshold or does not exceed a second voltage threshold.
7. 7. The power conversion circuit of claim 6, wherein the secondary control circuit further comprises: a first comparator for comparing the output voltage with the first voltage threshold value to generate a first comparison signal; A second comparator for comparing the upper second voltage threshold with the output voltage to generate a second comparison signal, and And an OR gate for performing a logical OR operation on the first comparison signal and the second comparison signal to generate the discharge signal.
8. 8. The power conversion circuit of claim 7, wherein the first comparator enables the first comparison signal when the output voltage exceeds the first voltage threshold; Wherein the first comparator disables the first comparison signal when the output voltage does not exceed the first voltage threshold; Wherein the second comparator enables the second comparison signal when the output voltage does not exceed the second voltage threshold; wherein the second comparator disables the second comparison signal when the output voltage exceeds the second voltage threshold; Wherein the or gate enables the discharge signal when the first comparison signal is enabled or the second comparison signal is enabled.
9. 9. The power conversion circuit of claim 6, wherein the second discharge circuit comprises: An output discharge resistor coupled to the output voltage, and And the discharge switch is used for coupling the output discharge resistor to the grounding terminal based on the enabled discharge signal so that the output discharge resistor discharges the output voltage.
10. 10. The power conversion circuit of claim 6, wherein the second discharge circuit comprises: An output discharge current source for generating a first current and coupled to the output voltage, and And a discharge switch for coupling the output discharge current source to the ground terminal based on the enabled discharge signal, so that the output voltage is discharged with the first current.
11. 11. The power conversion circuit of claim 6, further comprising: An optocoupler for generating a feedback voltage based on a feedback current; wherein the secondary control circuit generates the feedback current based on the output voltage; the control circuit generates the upper bridge driving signal and the lower bridge driving signal based on the feedback voltage and the resonance voltage.
12. 12. The power conversion circuit of claim 5, wherein the transformer further comprises: An auxiliary coil for generating an auxiliary coil voltage; wherein the power conversion circuit further comprises: a first voltage dividing circuit for multiplying the auxiliary coil voltage by a first voltage dividing ratio to generate a demagnetizing voltage; Wherein the control circuit generates the predetermined threshold value based on the demagnetizing voltage.
13. 13. The power conversion circuit of claim 1, wherein the power conversion circuit is a resonant flyback power conversion circuit.
14. 14. A control method, characterized by a power conversion circuit for controlling conversion of an input voltage to an output voltage, wherein the power conversion circuit comprises a resonant capacitor coupled between a resonant node and a ground, a transformer comprising a primary winding and a secondary winding, an upper bridge transistor for providing the input voltage to a switching node, and a lower bridge transistor for coupling the switching node to the ground, wherein the primary winding is coupled between the switching node and the resonant node, wherein the control method comprises the steps of: Simultaneously turning off the upper bridge transistor and the lower bridge transistor; After the step of turning off the upper bridge transistor and the lower bridge transistor simultaneously, determining whether a resonance voltage of the resonance node is lower than a predetermined threshold value, and When the resonance voltage is judged to be lower than the preset threshold value, the upper bridge transistor and the lower bridge transistor are driven to generate the output voltage.
15. 15. The control method according to claim 14, characterized by further comprising the step of: Judging whether the output voltage needs to be discharged or not; Discharging the output voltage when it is determined that the output voltage needs to be discharged, and And when the output voltage is judged not to be required to be discharged, the output voltage is not discharged.
16. 16. The control method according to claim 15, characterized in that the step of judging whether to discharge the output voltage further comprises the steps of: Judging whether the output voltage exceeds a first voltage threshold or does not exceed a second voltage threshold; Discharging the output voltage when it is determined that the output voltage exceeds the first voltage threshold or does not exceed the second voltage threshold, and When the output voltage is judged not to exceed the first voltage threshold and exceeds the second voltage threshold, the output voltage is not discharged.
17. 17. The control method according to claim 15, wherein the step of determining whether the output voltage needs to be discharged is performed simultaneously with the step of determining whether the resonance voltage is lower than the predetermined threshold value.
18. 18. The control method according to claim 15, wherein the step of determining whether the output voltage needs to be discharged is after the step of simultaneously turning off the upper bridge transistor and the lower bridge transistor, and before the step of determining whether the resonance voltage is lower than the predetermined threshold.
19. 19. The control method according to claim 15, characterized in that the step of discharging the output voltage further comprises the steps of: An output discharge resistor is coupled to the output voltage such that the output voltage is discharged through the output discharge resistor.
20. 20. The control method according to claim 15, characterized in that the step of discharging the output voltage further comprises the steps of: Drawing a first current from the output voltage such that the output voltage discharges at the first current.

Description

Power conversion circuit and control method thereof Technical Field The present invention relates to a power conversion circuit and a control method thereof, and more particularly to a resonant power conversion circuit and a control method thereof for simultaneously controlling a resonant voltage and an output voltage. Background With the continuous development of portable electronic devices, the development trend of power conversion circuits is as same as most power products, and the development trend is toward high efficiency, high power density, high reliability and low cost. Since the resonant power conversion circuit (including LLC resonant power conversion circuit, flyback power conversion circuit, etc.) is a high-efficiency and high-power-density power conversion circuit, the power conversion circuit of the portable electronic device is gradually oriented to the resonant power conversion circuit. However, current resonant power conversion circuits still have a number of drawbacks, and therefore further optimization of the resonant power conversion circuit is necessary. Disclosure of Invention The invention provides a power conversion circuit and a control method thereof, which are used for judging whether to discharge a resonant capacitor and an output capacitor after an upper bridge transistor and a lower bridge transistor are turned off so as to prevent the secondary coil of a transformer from generating surge and reduce the service life of elements. In view of the above, the present invention provides a power conversion circuit for converting an input voltage to an output voltage. The power conversion circuit comprises a resonant capacitor, a transformer, an upper bridge transistor, a lower bridge transistor and a control circuit. The resonance capacitor is coupled between a resonance node and a grounding terminal, wherein the resonance node generates a resonance voltage. The transformer comprises a primary coil and a secondary coil, wherein the primary coil is coupled between a switching node and the resonance node. The upper bridge transistor provides the input voltage to the switching node based on an upper bridge driving signal. The lower bridge transistor couples the switching node to the ground based on a lower bridge driving signal. The control circuit generates the upper bridge drive signal and the lower bridge drive signal based on the output voltage and the resonance voltage. When the upper bridge transistor and the lower bridge transistor are turned off, the control circuit judges that the resonance voltage is smaller than a preset threshold value, and then drives the upper bridge transistor and the lower bridge transistor. According to an embodiment of the present invention, the output voltage discharges faster than the resonant capacitor. According to an embodiment of the present invention, the power conversion circuit further includes a first discharging circuit and a second discharging circuit. The first discharge circuit discharges the resonance capacitor. The second discharge circuit discharges the output voltage. According to an embodiment of the invention, the first discharging circuit further includes a detecting resistor and a discharging resistor. The detection resistor is coupled to the resonant node. The discharging resistor is coupled between the detecting resistor and the grounding terminal. The control circuit adjusts the resistance value of the discharge resistor to adjust a discharge current for discharging the resonant capacitor. According to an embodiment of the present invention, the resonant voltage is divided by the detection resistor and the discharge resistor to generate a control voltage. The control circuit further comprises an analog-to-digital converter. The analog-to-digital converter is used for converting the control voltage into a digital code. The control circuit determines whether the resonance voltage is smaller than the predetermined threshold value based on the digital code. When the control circuit judges that the resonance voltage is smaller than the preset threshold value, the control circuit generates the upper bridge driving signal and the lower bridge driving signal. According to an embodiment of the present invention, the power conversion circuit further includes a rectifying circuit and a secondary control circuit. The rectifying circuit converts the energy of the secondary coil into the output voltage based on a gate signal. The secondary control circuit generates the gate signal. When the output voltage exceeds a first voltage threshold or does not exceed a second voltage threshold, the secondary control circuit enables a discharge signal. According to an embodiment of the invention, the secondary control circuit further includes a first comparator, a second comparison signal, and an or gate. The first comparator is used for comparing the output voltage with the first voltage threshold value to generate a first comparison signal. The secon